Previous workers in the crossbow art have used mechanical arrangements that allow the parts to work imprecisely, by using excessive parts that create excessive play. Play in any mechanism may reduce precision of location, and in a crossbow, mechanical play reduces precision of aiming.
One notable problem in the prior art is the use of movable cams and wheels located at the ends of movable parts, notably at the ends of the resilient limbs that store the energy used for shooting the arrow or bolt. A cam or wheel at the end of a limb moves during release of an arrow, and this is not conducive to precise aiming. Movement of the cam or wheel causes lateral acceleration of the tensile member engaging the cam or wheel, which causes addition imprecision and extra bearing friction. Moreover, friction in the cam or wheel bearing, if not precisely matched by that of the one on the other side of the crossbow, will throw off the aim, and precise matching the friction exactly is difficult. The same is true of any difference in spring constant, length, etc. between the two limbs (bow arms). Such differences will cause deflection of the arrow trajectory during the launch.